THE VOICE OF THE NORTH AMERICAN CONVEYOR INDUSTRY AGENDA OF THE CEMA ENGINEERING CONFERENCE CONVEYOR IDLER COMMITTEE MEETING Tuesday, June 26, 2012 – 8:30 AM 1. Call to order 2. Attendance and introductions – any new committee members? 3. Review and approval of previous minutes (attached) 4. Approval of Agenda 5. Old Business a. Kit “COLD TEMPERATURE TESTING” proposal b. CH 5 belt book requirements for next edition c. Idler roundness addition to 502 standard proposal 6. NEW BUSINESS a. OR meeting initiatives i. Dimensional standards for underground idlers ii. Metric belt width idler standards iii. Other ideas for their review 1. Idler roller standards 2. Roll gap standards 3. Kit test method included in the belt book b. Look at Kis testing – is the equation in 6 th edition over conservative. 7. ADJOURN Conveyor Equipment Manufacturers Association
Transcript
THE VOICE OF THE NORTH AMERICAN CONVEYOR INDUSTRY
AGENDA OF THE CEMA ENGINEERING CONFERENCE
CONVEYOR IDLER COMMITTEE MEETING
Tuesday, June 26, 2012 – 8:30 AM
1. Call to order 2. Attendance and introductions – any new committee members? 3. Review and approval of previous minutes (attached)
4. Approval of Agenda 5. Old Business
a. Kit “COLD TEMPERATURE TESTING” proposal b. CH 5 belt book requirements for next edition c. Idler roundness addition to 502 standard proposal
6. NEW BUSINESS
a. OR meeting initiatives i. Dimensional standards for underground idlers ii. Metric belt width idler standards iii. Other ideas for their review
1. Idler roller standards 2. Roll gap standards 3. Kit test method included in the belt book
b. Look at Kis testing – is the equation in 6th edition over conservative.
7. ADJOURN
Conveyor Equipment Manufacturers Association
THE VOICE OF THE NORTH AMERICAN CONVEYOR INDUSTRY
MINUTES OF THE CEMA ENGINEERING CONFERENCE
CONVEYOR IDLER COMMITTEE MEETING
Tuesday, June 28, 2011 – 8:30 AM
1. The meeting was called to order on Tuesday June 28th, 2011 at 8:30am by Jarrod Felton committee
chair a. (38) attendees representing (26) companies were present
2. Old Business
a. Metric conversion of 502 standard and CH 5 of belt book were reviewed. i. It was determined that all suggested changes be submitted to Jarrod Felton via
email by the end of August so it can be presented at the fall meeting b. The issue of the “E” dimension elimination from the V-Return dimensions in 502 was
reviewed. i. A voting ballot was not circulated to members as decided at the 2010 meeting,
because it was determined an illustration showing the result was required ii. An illustration of the V-return chart without the “E” dimension was submitted iii. A voting ballot will now go out to voting members
c. Kit “COLD TEMPERATURE TESTING” sub committee updates were presented i. The sub committee is to put together a proposal for the alterations to the belt-book
for Kit d. The issue of adopting an idler roundness standard was discussed
i. Tom Hubbert volunteered to draft a proposed addition to the 502 standard for review e. Decision on adding pipe conveyor idler standards to 502
i. There will be no additions to the 502 standard for pipe conveyor idlers at this time
NEW BUSINESS f. Kit test discussion
i. The issue is how to include a Kit test method to the Belt Book. g. Roll gap at center stands
i. The issue is whether 502 have include a standard for roll gap h. Potential Idler Roller standard
i. This will be a topic at the OR meeting in the fall i. Belt Book CH5 revisions reviewed
i. Send any input to Todd Swinderman or Jarrod Felton via email ii. Also, there will be some minor alterations made to make the 502 standard and the
Marty Yepsen Martin Engineering Company martyy@martin‐eng.com 309‐594‐2384
Conveyor Idler Committee Attendance List - 2011 CEMA Engineering Conference
BE
LT
CO
NV
EY
OR
ID
LE
R R
OL
LK
is'
TE
ST
PR
OC
ED
UR
EA P P E N D I X F
576
ForwardIntroductionScopeReferencesDefinitionsTest EquipmentTest Roll ConditionsTest ProceduresReportingRoll Status after Testing
BELT CONVEYOR IDLER ROLLKis' TEST PROCEDURE
BE
LT
CO
NV
EY
OR
ID
LE
R R
OL
LK
is ' TE
ST
PR
OC
ED
UR
EA P P E N D I X F
577
Foreword
This appendix provides a proposed procedure for determining the Kis' component of the resistance torotation of a single belt conveyor idler roll. The procedure is intended to provide a way of gathering dataon a uniform basis between various manufacturers to be used for conveyor power calculations.
1. INTRODUCTION
1.1 The Kx value is the total resistance to rotation of both the carrying and return idlers, in lbf per foot of conveyor length, as defined in the CEMA Publication Belt Conveyors for Bulk Materials, 5th
edition. The text from the 5th edition is included for reference in the 6th edition as Appendix C. Itincludes the resistance of the bearings to rotation due to load on the rolls. Kx combined the frictional resistance of the idlers and the sliding resistance between the belt and idler rolls.
1.2 Ai is used in the 5th edition as the component of the total resistance to rotation in lbs of the 3rolls of a standard troughing idler and a portion of the return roll (due to longer spacings) that isattributed to the resistance to turning due to the effects of all seals including any bearing seals,grease, including grease within the bearing, etc. In other words, all resistance to rotation that can not be attributed to the bearing resistance to rotation due to load. Ai is used in the calculation of Kx, in lbf per foot of conveyor length, as defined in the CEMA Publication Belt Conveyors for Bulk Materials, 5th edition and lower.
1.3 Combining load dependant rotational resistances and load independent resistances in one factor, Kx, results in a level of calculation precision that is less than satisfactory for many applications.In the 6th edition of Belt Conveyors for Bulk Materials the rotational resistance is broken downinto key components that can be evaluated independently. In the 6th edition the UniversalMethod for calculating conveyor power requirements the component Kis (in x lbf ) is the seal torsional resistance per roll at 500 rpm at a defined operating temperature. Kis' is the average value of Kis obtained from testing a representative sample of idlers following the Kis' test method.
2. SCOPE
2.1 This proposed CEMA Standard applies to the laboratory measurement of the Kis' component ofthe resistance to rotation of ‘dead’ or non-rotating (static) shaft belt conveyor idler rolls commonly used for the transport of bulk materials. This proposed standard test procedure applies to the steady state operation of rolls that have been run-in and is a statistical average innature. The aim of this proposed standard is to determine an accurate average value for the resistance to rotation at a defined rpm (excluding bearing resistance to rotation due to load) of the large quantity of idler rolls used in any belt conveyor, for power and belt tension calculation purposes.
3. REFERENCES
3.1 Applicable Publications- the following publications form a part of the specification to the extentspecified herein. Unless otherwise indicated, the latest revision of CEMA publications shall apply.
3.1.2 CEMA Publication Belt Conveyors for Bulk Materials, 5th edition and lower.
3.1.3 CEMA Publication Belt Conveyors for Bulk Materials, 6th edition and higher.
3.1.4 CEMA Standard No. 502 Bulk Material Belt Conveyor Troughing and Return Idlers.
BE
LT
CO
NV
EY
OR
ID
LE
R R
OL
LK
is'
TE
ST
PR
OC
ED
UR
EA P P E N D I X F
578
4. DEFINITIONS
The following definitions apply wherever the terms and expressions are used in this document:
4.1 Resistance to Rotation – The resistance to rotation of an idler roll is the torque or momentrequired to rotate the idler roll around a stationary shaft. It is calculated as the scalar sum of allcontact forces tangent to the test surface and parallel to the circumference generated by a pointon the test surface as it rotates, times the distance from the tangential force reaction to thecenterline of the idler bearings. This resistance is expressed in Chapter 6 of the 6th edition as achange in tension, ΔTis. To calculate ΔTis it is necessary to obtain a value for the factor, Kis thatis representative of the idlers to be used on the conveyor.
4.2 Test Speed - The test speed is the standard CEMA speed in revolutions per minute (rpm) asprovided in the load ratings for CEMA Standard Idlers. This is 500 rpm for all CEMA Series.Reference CEMA Standard No 502 Bulk Material Belt Conveyor Troughing and Return Idlers.
4.3 Ambient Temperature- - The term ambient temperature refers to the temperature of the airsurrounding the test roll(s) during a Kis' test. The ambient temperature is to be 75°F +/-10°.
4.4 Basic Test - The basic test is performed at the Basic Test Speed, at Ambient Temperature and inaccordance with all other requirements of this proposed standard.
5. TEST EQUIPMENT
It is not the purpose of this proposed standard to detail the test equipment used. The testequipment shall be suitable to accurately measure the resistance to rotation of an unloadedidler roll(s) during a basic test within +/-10%.
5.1 Test Methods - This proposed standard is intended to define the elements important to accurateand consistent measurement. Test machines will vary but there are two general methods withvarious sub-types that are considered acceptable. It includes the following two basic test method types each with sub-types:
In the Rotating Shell/Static Shaft method Types A, the shaft is stationary and the shell is rotated. This method most accurately replicates normal lubricant flow and rotation of the bearing rollingelements. However, the parasitic losses are significant and need to be accurately measured and subtracted from the measure value.
5.1.2.1 Method Type A-1.
Measures the reaction moment at the idler shaft using a force sensor or gauge and the result is converted mathematically to a Kis' value.
5.1.2.2 Method Type A-2.
Measures the reaction moment at the idler shaft using a reaction torque sensor or gauge andthe result is converted mathematically to a Kis' value.
5.1.2.3 Method Type A-3.
Measures the input torque to the test machine by various methods and the result is converted mathematically to a Kis' value.
In the Rotating Shaft/Static Shell method Types B, the shaft is rotated and the shell is heldstationary. This method does not accurately replicate normal lubricant flow and rotation of the bearing rolling elements. However, the parasitic losses are not very significant and in most cases can be ignored. This method’s overall accuracy is thus comparable to the Type A methods.
BE
LT
CO
NV
EY
OR
ID
LE
R R
OL
LK
is ' TE
ST
PR
OC
ED
UR
EA P P E N D I X F
579
5.1.3.1 Method Type B-1.
Measures the torque to turn the shaft using a rotary torque sensor or gauge and the result areconverted mathematically to a Kis' value.
5.1.3.2 Method Type B-2.
Measures the reaction force at the shell using a force type load cell or gauge and the result is converted mathematically to a Kis' value.
5.1.3.3 Method Type B-3.
Measures the reaction moment at the shell using a reaction torque sensor or gauge and theresult is converted mathematically to a Kis' value.
5.2 Multiple Roll Tests.
To reduce the time and effort required for a complete test, multiple rolls may be tested at onetime, where the test method type and test machine design allows. The Kis' value for such a testwill be the total resistance to rotation divided by the number of rolls in the basic test (i.e. asimple average).
5.3 Alignment and Load Control.
All roll alignments and load control during testing must be maintained so there is little or noeffect on the measurement of the resistance to rotation. These test parameters are typically:
• Near zero axial load on roll.
• Near zero normal load on roll.
• Near zero roll inclination angle.
5.4 Instrumentation.
The instrumentation used for readout, recording and if applicable, mathematical manipulationof test data, must be sufficiently accurate and precise as to provide rolling resistance measurements within +/- 10%.
6. TEST ROLL CONDITION
6.1 The roll to be tested must be in new condition. That is, either fresh off the production floor orfrom the warehouse. If the roll is from warehouse stock, then the roll is to have been in stockless than 1 year.
6.2 The roll may be any diameter, length, or type that falls within CEMA Standard No 502 BulkMaterial Belt Conveyor Troughing and Return Idlers.
6.3 For test methods Type A, the run-out of the test roll at the point of rotating load support mustbe with 0.015 inch Total Indicated Run Out (TIR). This is not necessary where the Type A Methodemploys a data acquisition system that has the proven ability to mathematically compensate forroll TIR problems. This is not necessary for Type B methods where the shell is held stationary.
6.4 All re-greaseable type rolls shall be properly greased with fresh grease before run-in. This meansrolls fresh from the production line and already properly greased maybe run-in directly. Rollsfrom stock, which are over 3 months old or if there is any question of the date of theirproduction, are to be fully purged and properly re-greased with fresh grease. Section 6.4 doesn’tapply to sealed for life products.
6.5 The roll is to be run in at 500 rpm +/- 10 rpm, for 100 hours +/- 10 hours, without load and in anambient temperature of 75°F+/-20°.
BE
LT
CO
NV
EY
OR
ID
LE
R R
OL
LK
is'
TE
ST
PR
OC
ED
UR
EA P P E N D I X F
580
6.6 After run-in, the roll is to have a thermal soak of at least 12 hours in the thermal environment of the test location prior to the test being performed to achieve thermal equilibrium.
6.7 If run-in is done within the thermal environment of the Kis' test, the test may proceed directly (within 30 minutes).
6.8 Run-in rolls may be tested up to 1 month after run-in.
6.9 If there is more than a 30 minute delay between run-in and test, the run-in roll is to be run for 30 minutes just prior to the Kis' test being performed on it.
6.10 Note: Any roll rework or other corrective action required should be undertaken before testing andwith care not to change the run-in characteristics of the roll.
7. TEST PROCEDURES
7.1 Basic Test.
The Basic Test will consist of the following 4 phases in sequence:
7.1.2 Initial Test Set-up:
7.1.2.1 Appropriately warm-up the test machine and all instrumentation.
7.1.2.2 Zero all instrumentation and/or record all instrumentation offsets.
7.1.2.3 Determine all parasitic losses of the test machine. Measurement of parasitic loss(es) is veryimportant and can be determined by different techniques depending on the equipment used.
7.1.3 Gross Resistance Measurement:
7.1.3.1 After running for 5 minutes measure resistance to rotation of the roll(s).
7.1.4 Check Validity:
7.1.4.1 Check for changes in the zero or instrumentation offset.
7.1.4.2 Determine that the total parasitic losses have not changed from 6.1.1.3.
7.1.4.3 From personal observation and the results of 6.1.3.1 & .2 above determine if the test is a valid one.
7.1.5 Data Manipulation:
7.1.5.1 Various types of machines and their instrumentation will have different methods in which thedata must be manipulated to arrive at the Kis' test value. The method must be a scientifically valid one.
7.1.5.2 Make certain that the effect of all instrumentation offsets have been taken into account inreducing/increasing the gross rotating resistance measured.
7.1.5.3 Also, make certain that all significant parasitic losses have been accurately determined and aresubtracted from the gross rotating resistance measured in 6.1.2 after instrumentation offsets have been taken into account.
7.1.5.4 If multiple rolls are tested divide the net resistance to rotation by the number of rolls in the basictest to get the Kis' test result for the basic test.
7.1.5.5 Kis' results at the test diameter shall be adjusted for the other standard CEMA roll diameter(s) by assuming the rolling resistance is inversely proportional to the roll diameter. The test value shall be adjusted by the following equation:
BE
LT
CO
NV
EY
OR
ID
LE
R R
OL
LK
is ' TE
ST
PR
OC
ED
UR
EA P P E N D I X F
581
7.2 Complete Test.
A complete test will involve statistically significant quantities of rolls, minimum of 20. Anycombination of roll diameters, lengths, and roll types may be used towards a complete statisticaltest. However, all rolls must have the same construction details that would affect the Kis' value.Obviously, all results must be referred to one diameter for the statistical average being tested for.
A complete test will produce one result, a single Kis' value. This value will be the average of all the resistance to rotation measurements for all basic tests completed.
Where multiple rolls are tested in a single basic test, the result is an average. The test results foreach of these multiple roll tests may simply be averaged to arrive at a complete test average, thesingle Kis' value.
8. REPORTING
As a minimum the report shall consist of the following:
8.1 Roll Identification.
8.1.2 The following information for the identification of each complete test should be recorded, if applicable:
8.1.2.1 Manufacturer and/or Supplier.
8.1.2.2 Brand name and/or Trade Name and/or Roll Series.
8.1.2.3 CEMA Class.
8.1.2.4 Roll Type(s) (steel, rubber disc, rubber tire, etc.) .
8.1.2.5 Roll(s) diameter(s) tested.
8.1.2.6 Grease details.
8.1.2.7 Standard construction details.
8.1.2.8 Any special construction details (ex. with splash guard, weather shield, stone guard, etc.).
8.2 Test Results.
8.2.2 The following complete test information shall be reported:
8.2.2.1 Kis'[test] at the CEMA diameters tested.
8.2.2.2 Kis'[other] at all standard CEMA diameters for the Class of roll tested.
8.2.2.3 Test method type.
8.2.2.4 Any special test details (ex. multiple roll tests, number of rolls per test, etc.
8.2.2.5 Test month and year.
9. ROLL STATUS AFTER TESTING
Tested rolls are to be considered still in new condition and may be returned to stock.
1
ROLL CONCENTRICITY TOLERANCE Roll concentricity tolerance (also called peripheral runout and circular runout) is intended to provide a measure of how well a roll achieves roundness, straightness, and centering with respect to the shaft centerline. Concentricity tolerance testing can catch problems such as flat spots, ovality, poor weld seam finish, distortion due to welding, taper, bowing, and poor roll end disk positioning. Controlling roll concentricity tolerance is important in reducing conveyor noise levels. A concentricity test involves positioning three dial indicators in a radial fashion along a roll supported by its shaft. Two indicators are located usually 25mm to 30mm from each end while one indicator is positioned at the roll center. As the roll is rotated about its axis 360 degrees, the difference between the largest and smallest deflection is noted at each of the three locations (Figure 1).
Figure 1
Readings taken from the ends of steel and lagged rolls are typically not allowed to exceed 0.5mm. Commonly acceptable center readings for steel rolls are represented in Table 1. In general, larger concentricity tolerance values are allowed as the roll diameter and roll length increase. For steel rolls, allowable center values can range from 0.5 mm to 2.3 mm. If the rolls are lagged, an additional allowance for the center reading of 1mm is added to the allowable values of Table 1. For scale rolls, the concentricity tolerance is limited to a maximum value of 0.15mm to 0.38mm. Obtaining these values for scale rolls may involve machining the face of the roll, which may require rebalancing the rolls due to resulting non-uniform shell wall thickness.
Max. Concentricity Tolerance
mm
Roll Length mm
Diameter ≤ 133
Diameter > 133
≤ 530 0.5 0.6 600 to 900 0.7 0.9
1050 to 1400 1.3 1.6 1400 to 2500 1.9 2.3
Table 1
2
PERMISSIBLE ROLL UNBALANCE Roll unbalance can cause undesirable vibrations leading to increased noise and premature bearing failure. The standard commonly used for acceptable unbalance in idler rolls is ISO 1940-1. This standard defines balance quality grades from G0.4 to G4000. The magnitude of the balance quality grade indicates the permissible amount of unbalance (mm/s). The intensity of the unbalance (mm/s) is defined as = ×
Where n = Rotating Speed, rpm G = Out of Balance Mass, g r = Roll Radius, mm M = Mass of Rotating parts, g For standard steel idler rolls, a quality grade of G40 is considered acceptable. For scale quality rolls, a quality grade of G16 is considered acceptable. Figure 2 shows a typical test machine designed to measure unbalance in rotating equipment. The roll is usually tested at the rotating speed for the actual application. This is a non-destructive test and can be easily implemented into a Quality Test Plan during production.
Figure 2
Idler Seal Drag: The support idlers resist rotation and belt movement by mechanisms internal to the idler roll. Idler seal and lubricant friction are independent of load and this section addresses their contribution to drag. Idler bearing related losses are covered later in the load dependent section. CEMA member products were independently tested and the published values represent safe steady state running idler seal drag for design of most conveyors, independent of the member product selected. Special cases exist and are discussed below. Idler seal drag is defined as a torsional moment restraining the shaft with an equal and opposite shell force acting on the roll radii moment arm, reference Figure 6.16. Published values represent the maximum expected steady state mean seal drag of a population of rolls that have been broke in. CEMA tests have shown seal drag is dependent upon roll speed, component sizes, design paradigms, ambient temperature and roll condition.
Figure 6.16 Idler belt line reaction Torsional moments are published as linear curve fit coefficients in a per roll format as shown in Figure 6.17A. Kis is the moment at 500rpm and Kiv is the slope to estimate other speeds. Components become heavier with increases in the CEMA load series and published drags increase accordingly, as shown in Table 6.19. The equation in Figure 6.17B gives the drag per roll as a force at the shell/belt interface. The equation in Figure 6.17C can then be used to calculate the total drag of each roll type in the flight.
0
1
2
3
4
5
6
0 100 200 300 400 500 600 700 800
RPM
DR
AG
FO
R O
NE
RO
LL
(in
-lb
Kis = torque @ 500rpm
Kiv = slope of line
Figure 6.17A Graph of single roll drag linear curve
where;
Figure 6.17B Single roll idler seal friction equation
Figure 6.17C Idler seal friction equation for one flight Where: ∆Tis (lbf / N) = belt line tension from seal drag for one roll ∆Tisn (lbf / N) = belt line tension from seal drag for rolls in carry or return flight Kiv (in-lbf/rpm) = slope of single roll torsional speed curve – Table 6.19 A&B (Nm/rpm) Kis (in-lbf / Nm) = seal torsional drag for one roll at 500rpm – Table 6.19 A&B
KiT = temperature correction factor – Figure 6.18A, & B Kita & Kitb = curve fit constants for temperature correction – Table 6.19 A&B V (ft/min / m/s) = belt speed nr = number of rolls in idler set for the carry or return flight Dr (in / mm) = roll diameter Tf (°F / °C) = Ambient operating temperature Ni = Roll speed (rpm) Sin (ft / m) = Carry or return idler set spacing in a flight Ln (ft / m) = Length of flight “n”
CEMA C & D Kit vs Temperature
0
0.5
1
1.5
2
2.5
3
3.5
-40 -25 0 15 35 55 75 95 115
Temperature (°F)
Kit
Historical
Current
CEMA E Kit vs Temperature
0
0.5
1
1.5
2
2.5
3
3.5
-40 -25 0 15 35 55 75 95 115
Temperature (°F)
Kit
Hist or ical
Current
Figure 6.18A Temperature correction factor graphs Ambient temperature has a significant impact on idler seal drag and the multiplying factor, Kit, accounts for it. CEMA member products have been independently tested and the equations published reflect seal drag change with temperature. This work is graphically shown in Figure 6.18A. For lower load rated products the primary difference is in the mid-range temperatures. Higher rated products also show a
change at lower temperatures. CEMA published Kit values should only be used with published Kis and Kiv values. Testing shows designs can vary widely and using design specific Kis or Kiv values with the Kit calculated by equations in Figure 6.18B can drastically misrepresent true performance.
Figure 6.18B Temperature correction equation
CEMA members have different seal design philosophies and significant drag variances exist, see Figure 6.19. Common variables are geometry, materials, contact seals and grease viscosity/amount/location. Drag variance adjustment factors provide a means to include this when appropriate. All conveyors should be analyzed with Rriv=Rris=1.0. In the following special cases, an additional analysis is recommended using Rriv=0.0 and Rris=0.4, which gives power estimates at the lower range of member products. These values should NEVER be applied when using actual drag values for a particular design. Keep in mind it is important to coordinate use of adjustment factors in all sections of the Universal Power Calculations.
• Conveyors where minimal power is from elevation change with long length and thousands of rolls. (i.e. flat overland conveyors)
• Downhill conveyors where lower seal drag could create a regenerative situation. • Conveyors with significant horizontal curves, where tension control at specific locations may be
of benefit.
Comparison of Independent Tests to CEMA E Ratingsat Kit=1.0
0
1
2
3
4
5
6
7
8
9
100 200 300 400 500 600
Roll Speed (rpm)
Sea
l Dra
g (
in-l
bf)
Upper Rating Limit (Rris = Rriv = 1.0)
Low er Rating Limit (Rris = 0.4; Rriv =0.0)
Multiple rolls used for each test series and results show n represent the average for the
CEMA Rating in Hatched Area
Figure 6.19 Example of actual roll test versus CEMA rating The idler rotating resistance varies over it’s lifetime from a high torque during break-in when new to easy rolling during prime operation to high resistance at failure. After break-in, when starting a stationary roll a higher breakaway resistance is experienced which drops off to the steady state value after a few minutes of warm-up. At times it is advantageous to use actual seal drag values for a particular product. When doing this it is important to keep in mind each design has its own characteristics and acquiring an understanding of the particular Kis, Kiv, Kt, Rris and Rriv is recommended. CEMA testing has shown applying these factors to any particular roll design creates significant error. All designs are unique and the variance adjustment factors presented do not apply to a particular design.
![Centers for Turning and Grinding - Powerhold, Incpowerholdinc.com/uploads/products/21_CarbideDeadCenters[1].pdf · Carbide dead centres Roundness achieves roundness When grinding,](https://static.documents.pub/doc/80x56/5a7e878f7f8b9a66798e90ae/centers-for-turning-and-grinding-powerhold-1pdfcarbide-dead-centres-roundness.jpg)
